Broken headstuds. Inevitable?

[ertech]

Got a 89 turbo did they fix the divlars by 89?
Thanks

[porwolf]

In what years were Dilivars actually installed by the factory?

[shbop]

Originally Posted by ertech

Got a 89 turbo did they fix the divlars by 89?
Thanks

Just re-built the top on an 88' Carrera. Not a turbo, but all exhaust studs were divilar. None were broken with 70K miles, but wasn't willing to chance their future. Changed them out for steel.

[markwemple]

I think the factory did ex side dilavars on all SCs and Carerras.

[j911brick]

Originally Posted by markwemple

I think the factory did ex side dilavars on all SCs and Carerras.

Not true.

[markwemple]

So when? All I've seen were/are.

[j911brick]

Originally Posted by markwemple

So when? All I've seen were/are.

and i have never seen any. Go figure.

[Bob Kontak]

Originally Posted by Flat6pac

I ve retorqued heads with the dilivars in place..dont put the valve covers on so you can pick up the pieces in the morning.
Bruce

Good one.

FWIW - I installed Raceware in 96. Top and bottom. Washers and nuts, too. Had I known more about lower cost acceptable alternatives I would have gone that route.

[Laneco]

Steve and I have bought 6 used 911 engines through the years. One 2.4, two 3.2's and three 3.0's.

All three 3.0's had two or more broken head studs. I figure the 3.2's were just luck of th draw (2.4's not prone).

So the easiest way to tell if the head studs will break or are already broken on a 3.0 is to sell the engine to me - LOL!

angela

[KTL]

The steel/Dilivar combo started in 1974 according to the PET parts reference. The combo was on the naturally aspirated engines. The 930/turbo engines have always spec'd all Dilivar. Note that the original Dilivar stud part number from 74-89 changed once. It began as 930.101.170.00 from 74-77 and in 78 they changed it to 930.101.170.02 which carried that part number all the way thru the 964 until the 993 all-thread came along.

In 1989 with the intro of the 964 3.6, they were all Dilivar on the 3.6 N/A and also on the 964 3.3 turbo. This stud was the same 930.101.170.02 part number as the 78-89 911 engines. The 964 turbo 3.6 used 12 of the 930.101.170.02 Dilivar and 12 of the newer 993 Dilivar stud which was 993.101.170.51

Then when the 993 3.6 came along, Porsche threw us a curve again and installed all steel 993.101.172.02 on the regular 3.6 N/A. I recently bought some of these and they're indeed inexpensive steel, now superseded to 993.101.172.03. Porsche revised the Dilivar install on the 993 twin turbo 3.6 to have all 24 studs be the 993.101.170.51, which is currently superseded by 993.101.170.53- the fully threaded stud. Note that the 993 RS also used all 24 Dilivar studs. The 993 all-thread stud is the only current Dilivar offering from Porsche, which is $42 each

To add further to the stud chronology, Porsche used a 996.101.172.70 stud on the 996 turbo and 996 GT3. Many may recall that this engine case is based on the 964 case. So it has head studs like our old engines. This stud must be steel because it's only $16 each. Heat influence on the 996 studs is probably much less, given the water cooling system, so no need for the fancy Dilivar?

Just for grins (ha ha, i'm sure everybody is having tons of fun here.....) I looked up the 959 stud. 959.101.170.02 is unknown material but it's only $33 ea. so i'm guessing it's steel?

I'm no expert engine builder that knows all this from experience. I simply pulled all this information from the parts diagrams.

[G450X]

For the Dilivar saga Kevin, that's a nice synopsis.

The 959 stud info is interesting, almost worth buying them for bragging rights "case rebuilt with 959 studs...."

Although I've heard of a few steel failures, I assume there's probably no reason to go high dollar (ARP, etc.) on studs at a rebuild unless you have an uber high performance engine?

[porwolf]

Thanks here also for your thorough Dilivar research, Kevin. So, do you think my stock California 79 SC may have been spared of the Dilivars?

[KTL]

Be careful with the 959 or 996TT/GT3 studs. Their different head design likely has a different stud length that is not compatible with out air cooled junk.

I've heard a rule of thumb that 300 crank HP is the limit of steel studs. I think Walt Fricke mentioned he got that bit of advice from one of the highly experienced engine builders.

The parts diagrams say all '79 SC had the steel-Dilivar combo. There's no separate listings of head studs for the 930.04 USA '79 engine and the 930.06 CA '79 engine.

[porwolf]

Thanks Kevin! Your depth of knowledge blows me away. So the 79 SC engines come with a Dilivar/steel combination. Which studs are used where? Upper steel, lower Dilivars?

[KTL]

Yep. Steel on top and Dilivar on the bottom.

I have 21 Dilivars (well used, none broken, still shiny black paint) if anybody wants to roll the dice on a set of 12 for the bottom. The other three were slotted on the threads to use as thread chasers in the engine case threads.

I personally wouldn't reuse a Dilivar for the reason Bruce mentioned above. That said, when I did the top end on my '87 and a friend's '88 3.2, we left all the studs alone and reinstalled the heads with no problems of snapped Dilivars (yet...... *knock on wood skull*)

[88-diamondblue]

Did my rebuild on my engine due to one broken stud on each side. An 1988 with 88,000, stored winters in heated garage and well cared for. They were the black coated ones. I believe that given enough time dilvar will fail. Used steel on mine and it has been fine.

There was an older thread that someone had that torqued the new dilivar studs and came back in the morning with at least one that broke. I liked doing my rebuild but not enough to chance doing it again

[SCadaddle]

A few weeks ago we removed the lower row of head studs on my 82SC. The one that was obviously broken in half and found 2 more that were "on the tear". All but the one that was broken in half were removed with the SnapOn collett tool and considerable heating. I was very surprised the two "torn" ones survived the mission.

[SCadaddle]

[jackb911]

My '87 broke one at 117K miles, replaced with a full set of ARP's.

[j911brick]

I just puled apart a '82 race car with about 100k miles and to spite the fact the nuts were on pretty tight none of the dilivars were broken. Looks like this motor has never been opened up.